The present invention relates to novel curable compositions based on silicon-containing butadiene polymers.
Ordinary polybutadienes or copolymers of butadiene as the main component which can be obtained by polymerization in bulk, solution, or in emulsion generally have ethylenically unsaturated linkages in their molecular structure and readily cure with heat through crosslink formation in the presence of an organic peroxide. The cured products has excellent electric and other physical properties, by virtue of which they enjoy a wide field of applications including molding and impregnation of electric parts and the like.
The above polybutadienes and copolymeric butadiene polymers, which usually are liquid at room temperature, have the following disadvantages.
(1 ) The viscosity of polymer tends to greatly increase, sometimes to a degree enough to form a non-flowing mass and lower workability, when a siliceous filler is added.
(2) The viscosities of polymers vary within a wide range depending on temperatures.
(3) The curing reaction of polymer is very exothermic, while volume shrinkage is large.
(4) The adhesive bond of polymer after cure to substrate is poor.
(5) The cured products obtained from the polymers have inferior heat stability and resistance to oxidation.
(6) The cured products with a higher content of 1,2-polybutadiene structure in the molecular structure are usually brittle and poorly flexible, and tend to crack, while those with a higher content of 1,4-polybutadiene structure in the molecular structure are less reactive and less curable.